The disclosure concerns a digital printer to print a recording medium with toner particles that are applied with the aid of a liquid developer, in particular a high-speed printer to print web-shaped or sheet-shaped recording media.
In such digital printers, a latent charge image of a charge image carrier is inked by means of electrophoresis with the aid of a liquid developer. The toner image that is created in such a manner is transferred indirectly (via a transfer element) or directly to the recording medium. The liquid developer has toner particles and cleaning fluid in a desired ratio. Mineral oil is advantageously used as a cleaning fluid. In order to provide the toner particles with an electrostatic charge, charge control substances are added to the liquid developer. Further additives are additionally added, for example in order to achieve the desired viscosity or a desired drying behavior of the liquid developer.
Such digital printers have been known for a long time, for example from DE 10 2010 015 985 A1, DE 10 2008 048 256 A1 or DE 10 2009 060 334 A1.
To ink the charge images on the charge image carrier, liquid developer is directed past the charge image carrier by a developer station. The developer station has a developer roller (the manner is known per se) that directs the liquid developer past the charge image carrier; an application system that supplies the liquid developer to the developer roller; and a cleaning unit that cleans off the residual liquid developer that remains on the developer roller after the inking of the charge images at the charge image carrier. For example, the cleaning unit provides a cleaning roller that removes the residual liquid developer from the developer roller; an electric field thereby exists between developer roller and cleaning roller, for example, which electric field promotes the transfer of the residual liquid developer. The residual liquid developer can be scraped off the cleaning roller by a blade. No residual liquid developer should thereby remain on the cleaning roller, since otherwise it could arrive again at the developer roller.
Developer stations are known in which liquid developer is supplied to a charge image carrier. In U.S. Pat. Nos. 7,522,865 B2, 7,292,810 B2, 6,895,200 B2, developer stations are described in which liquid developer is directed past a developer roller. Arranged adjacent to the developer roller is an electrode. The liquid developer is directed between the electrode and the developer roller. An electric voltage exists between the electrode and the developer roller, via which electric voltage the toner is drawn towards the developer roller.